He joined the U.S. Army and fought in North Africa and Europe during World War II. Robertson was wounded twice and awarded the Bronze and Silver Stars and the Purple Heart.
While stationed at San Luis Obispo, Calif., he had a photograph taken for his mother. A copy of the photo displayed in the photo shop window attracted movie scouts, and the 6-foot-tall, 180-pound Robertson soon was on his way to Hollywood.
Will Rogers Jr., son of fellow Oklahoma-born actor and writer Will Rogers, once told Robertson to avoid formal training and keep his own persona.
Robertson received the Golden Boot Award in 1985, and was inducted into the Hall of Great Western Performers and the Cowboy Hall of Fame in Oklahoma City.
He was married several times, most recently in 1980 to Susan Robbins, who survives him along with two children.
Nancy Robertson said her uncle will be cremated and that a memorial service will be held in a few weeks.
Former Associated Press writer Rochelle Hines contributed to this report.